There has heretofore been known a device housing package having an input-output terminal comprising a dielectric layer with a signal line formed on one main surface thereof and a ground layer formed on the other main surface thereof (refer to Japanese Unexamined Patent Publication JP-A 8-227949 (1996), for example). Currently, there is an increasing demand for a device housing package which is, even if a signal to be transmitted through a signal line falls in a high-frequency range such as a microwave range or a millimeter-wave range, capable of affording excellent high-frequency transmission characteristics while minimizing electromagnetic-wave leakage. An object of the invention is to provide a device housing package which excels in high-frequency transmission characteristics and a mounting structure using the device housing package.